[llvm] [llvm][InstCombine] Fold signum(x) into scmp(x, 0) (PR #143445)

[Craig Topper via llvm-commits]

topperc wrote:

> > > Irrelevant to this PR in itself, but I did notice when running both src in tgt in llc, but why does llc lower the src in the alive2 posted better than the intrinsic?
> > 
> > 
> > I'm guessing you mean on X86. It looks neutral on RISC-V and scmp looks better for AArch64.
> 
> Yeah, might have to work on that.
> 
> I mean human written asm for this in particular is:
> 
> ```
>   add edi, edi
>   setnz cl
>   sbb eax, eax
>   or al, cl
>   ret
> ```
> 
> but I do not know if I can get the compiler to lower that to this.

`add edi, edi` seems wrong there

https://github.com/llvm/llvm-project/pull/143445